KR100595947B1 - High strength thin steel sheet, high strength galvannealed steel sheet and manufacturing method thereof - Google Patents

Abstract

0.005 (단, T_b : 밴드형 조직의 판두께 방향 평균두께, T : 강판 두께) 의 관계를 만족시키는 두께인 가공성, 도금성이 우수한 고강도 박강판 및 그 제조방법, 그리고 용융아연도금 또는 합금화 용융아연도금을 하는 우수한 가공성과 고강도를 지님과 동시에 우수한 도금성, 도금 밀착성, 내식성을 얻을 수 있는 고강도 용융아연도금 강판 또는 고강도 합금화 용융아연도금 강판의 제조방법.C: 0.01-0.20 wt%, Si: 1.0 wt% or less, Mn: 1.0-3.0 wt%, P: 0.10 wt% or less, S: 0.05 wt% or less, Al: 0.10 wt% or less, N: 0.010 wt% or less , Cr: 1.0 wt% or less, Mo: 0.001-1.00 wt%, and the remaining portion is composed of Fe and inevitable impurities, and the band structure composed of the second phase is T _b / T

High-strength thin steel sheet with excellent workability and plating property and its manufacturing method, and a hot dip galvanized or alloyed melt, satisfying the relationship of 0.005 (T _b : average thickness in the thickness direction of the band-like structure, T: steel sheet thickness) A method for producing a high strength hot dip galvanized steel sheet or a high strength alloyed hot dip galvanized steel sheet, which has excellent workability and high strength for galvanizing and at the same time obtains excellent plating, plating adhesion and corrosion resistance.

High strength thin steel sheet, high strength alloyed hot dip galvanized steel sheet

Description

High strength thin steel sheet, high strength alloyed hot dip galvanized steel sheet and manufacturing method thereof {HIGH STRENGTH THIN STEEL SHEET, HIGH STRENGTH GALVANNEALED STEEL SHEET AND MANUFACTURING METHOD THEREOF}

The present invention provides a high strength steel sheet (plating mother plate) suitable for use as an automobile body, and the like, and a high strength alloyed hot dip galvanized steel sheet and a high strength thin steel sheet, a high strength hot dip galvanized steel sheet and a high strength alloyed hot dip galvanized steel sheet It relates to a manufacturing method of.

In recent years, from the viewpoint of improving the global environment in addition to the stability, light weight and low fuel consumption of automobiles, the application of high strength steel sheets and high strength hot dip galvanized steel sheets excellent in corrosion resistance as automotive steel sheets has been increasing.

Among them, in order to manufacture a high strength hot-dip galvanized steel sheet, it is necessary to prepare an original plate which has good plating property, passes through a hot-dip galvanizing bath, and obtains the desired strength and workability after the heat alloying treatment is performed.

In general, in order to increase the strength of the steel sheet, solid solution strengthening elements such as P, Mn, and Si, and precipitation strengthening elements such as Ti, Nb, and V are added.

When the steel sheet to which the above element is added is treated in a continuous hot dip galvanizing line (CGL), the steel sheet is annealed at a temperature of Ac ₁ transformation point or higher, and the cooling rate is slow, so that high strength is hard to be obtained. The cost is high because alloying elements have to be added.

In addition, it is known that the addition of a large amount of alloying elements significantly degrades the galvanizing property, and the addition amount of the alloying elements is limited in view of the plating property.

Since alloy elements in the base steel sheet have opposite effects on strength and plating property, it is very difficult to produce high strength hot dip galvanized steel sheet having good plating properties in a continuous hot dip galvanizing line.

Moreover, in the case of a high strength steel sheet, since the characteristics regarding workability, such as elongation, are inferior, it was more difficult to manufacture the hot-dip galvanized steel plate with favorable workability.

On the other hand, as a high strength steel plate with good workability, a conventional composite steel sheet including a low temperature transformation phase (including residual austenite) containing martensite as a main phase in ferrite substrates has been proposed.

The composite steel sheet has a low yield ratio [: {yield strength (YS)} / {tensile strength (TS)} at room temperature and no aging, and is excellent in workability and baking hardening after processing.

As a method for producing a composite steel sheet, a method of heating at (α + γ) inverse temperature and then rapidly cooling with water or gas cooling is known. The faster the cooling rate, the more the alloy element type and the amount of alloying are required. It is also known to be at least.

However, in the conventional composite steel sheet, when hot dip galvanized or heat-alloyed at a temperature of about 500 ° C., hard martensite of the second phase other than the first phase ferrite is not produced, and soft cementite, pearlite, and bay are produced. As the nitrate is formed, the tensile strength is lowered, an upper yield point appears, an increase in the yield ratio, and a yield extension occurs.

Tempering softening is more likely to occur when there are fewer alloying elements, such as Mn and Si, and, on the other hand, when there are many alloying elements, hot dip galvanizing property falls.

As a result, hard martensite is not produced in the plating process even in the composite steel sheet, and soft cementite, pearlite, and bainite are produced. Therefore, both the workability by the ferrite phase of the first phase and the high strength by martensite of the second phase are achieved. In addition, it was difficult under the prior art to exhibit good plating properties.

On the other hand, in a plated steel sheet, it is necessary to be excellent in the plating adhesiveness of a plated steel sheet so that a metal mold | die may not be acquired while preventing the plating peeling at the time of press working.

In general, in order to increase the strength of the steel sheet, it is generally made to add a solid solution element (dioxide element) such as Mn as described above. As a result, a so-called non-plating defect occurs on the surface of the steel sheet, which is concentrated on the surface of the steel sheet and degrades the wettability with molten zinc. As a result, plating is hardly adhered to the steel sheet surface.

The recrystallized annealing atmosphere is a reducing atmosphere in Fe and Fe oxide is not produced, but in an oxide element such as Mn, it becomes an oxidizing atmosphere, and these elements are concentrated on the surface of the steel sheet to form an oxide film. This is because it lowers.

As a method for producing a high strength hot-dip galvanized steel sheet, Japanese Patent Laid-Open No. 55-50455 discloses a method for specifying a cooling rate after annealing when plating, but the method is not mentioned at all in the method of improving the plating property. In particular, when the Mn content of the base steel sheet exceeds 1%, it is difficult to prevent the plating from being prevented, and there is no mention of a method of improving the plating adhesion.

Therefore, it is a fact that the high-strength steel plate excellent in workability which is attractive as a high strength material for automobiles also lacks the practical means for use as a surface-treated steel plate which is hot-dip galvanized and excellent in workability and also excellent in plating adhesiveness.

In addition, Japanese Patent Application Laid-Open No. 7-9055 discloses a method of improving the alloying speed of P-added steel after galvanizing after annealing after annealing, but the method is for improving the alloying speed. It is not a method for preventing the plating from failing.

In addition, the above-mentioned method does not mention the dew point, the hydrogen concentration, and the temperature of the atmosphere gas at the time of annealing immediately before the plating, and it can be seen that many of the platings are not generated under the combination condition of the steel type and the annealing atmosphere.

In Japanese Patent Laid-Open No. 7-268584, a method of secondary annealing is disclosed at a temperature determined by the P content in steel, but it is a technical idea that the temperature range for preventing steel sheet embrittlement depends on the P content in steel. It is based on, and is not disclosed about the temperature for making plating property favorable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems in the prior art, and is capable of achieving excellent workability and high strength, and excellent plating properties and excellent corrosion resistance even after hot dip galvanizing or heat alloying treatment. An object of the present invention is to provide an alloyed hot-dip galvanized steel sheet excellent in workability, plating adhesion, and corrosion resistance using a high strength thin steel sheet as the base steel sheet, and the high strength steel sheet.

A specific object of the present invention is an index indicating workability and high strength, and has a yield ratio of 70% or less and a TS × El value of 16000 MPa ·% or more, while having a high strength steel sheet having excellent workability that can prevent occurrence of unplated defects. And a high strength alloyed hot dip galvanized steel sheet and a high strength thin steel sheet, a high strength hot dip galvanized steel sheet, and a high strength alloyed hot dip galvanized steel sheet having excellent workability, plating adhesion, and corrosion resistance using the high strength thin steel sheet.

Disclosure of the Invention

MEANS TO SOLVE THE PROBLEM The present inventors discovered the following knowledge (1)-(4) as a result of earnestly researching for the said subject.

(1) Dispersion of Band Structure in Steel Sheet:

In view of improving the mechanical properties, at the same time using a predetermined composition steel sheet and heating the steel sheet to a predetermined temperature or more, in particular, in the second phase (mainly cementite, pearlite, bainite and very part of martensite and residual austenite) By disperse | distributing the band structure which consists of) to a predetermined range, the thin steel plate which is compatible with workability and high strength, and has favorable plating property can be obtained.

(2) two-stage heating and pickling method:

In view of further improving the plating property, the steel sheet of the predetermined composition is used, and the steel sheet is heated and cooled in the annealing furnace to a predetermined temperature or more, and then the concentrated layer of the steel component on the surface of the steel sheet is removed by pickling, followed by continuous melting. After annealing in a galvanizing line again at a predetermined reducing atmosphere at a predetermined heat reduction temperature, hot dip galvanizing can be used to obtain a high strength hot dip galvanized steel sheet which is excellent in workability, plating adhesion and corrosion resistance while preventing plating defects. .

That is, in the method of reducing annealing the steel sheet once annealed again, an important matter in order to secure the plating property is the atmosphere at the time of reduction annealing.

If the P-based pickling residue generated on the surface of the steel sheet is not sufficiently reduced when pickling the steel sheet once annealed, an oxide film having poor wettability with molten zinc inhibits the plating property of the steel sheet immediately after annealing. In the method for producing a high strength hot dip galvanized steel sheet of the present invention, the annealed steel sheet is annealed again at a predetermined heat reduction temperature in a predetermined reducing atmosphere, followed by hot dip galvanizing.

(3) one-stage heating treatment method:

As a result of further studies by the present inventors, it has been found that after the steel sheet is heated in an appropriate dew point atmosphere gas at an appropriate heating temperature and then hot-dip galvanized, good plating property, workability and plating adhesion can be obtained in one step of heating.

(4) alloying treatment method:

By alloying the hot-dip galvanized steel sheet obtained in the above (1) to (3), preferably under conditions satisfying a predetermined alloying temperature, a high-strength alloyed hot-dip galvanized steel sheet excellent in both plating adhesion and corrosion resistance after alloying can be obtained. .

More preferable aspect of this invention of following (1)-(39) and this invention is completed based on said knowledge (1)-(4).

0.005 (단, T_b : 밴드형 조직의 판두께 방향 평균두께, T : 강판 두께) 의 관계를 만족시키는 두께인 것을 특징으로 하는 가공성 및 도금성이 우수한 고강도 박강판.(1) C: 0.01-0.20 wt%, Si: 1.0 wt% or less, Mn: 1.0-3.0 wt%, P: 0.10 wt% or less, S: 0.05 wt% or less, Al: 0.10 wt% or less, N: 0.010 A band-like structure composed of wt% or less, Cr: 1.0 wt% or less, Mo: 0.001-1.00 wt%, the remainder of which is composed of Fe and an unavoidable impurity, and the second phase has a T _b / T

A high strength steel sheet excellent in workability and plating property, characterized by a thickness satisfying a relationship of 0.005 (T _b : average thickness in the thickness direction of the band-like structure, T: steel sheet thickness).

(2) In (1), the high strength steel sheet further contains one or two or more selected from Nb: 0.001-1.0 wt%, Ti: 0.001-1.0 wt%, and V: 0.001-1.0 wt%. High strength steel sheet with excellent workability and plating.

0.005 (단, T_b : 밴드형 조직의 판두께 방향 평균두께, T : 강판 두께) 범위로 조정하는 것을 특징으로 하는 가공성 및 도금성이 우수한 고강도 박강판의 제조방법.(3) C: 0.01-0.20 wt%, Si: 1.0 wt% or less, Mn: 1.0-3.0 wt%, P: 0.10 wt% or less, S: 0.05 wt% or less, Al: 0.10 wt% or less, N: 0.010 wt% or less, Cr: 1.0 wt% or less, Mo: 0.001 to 1.00 wt%, the remainder being hot rolled to a slab composed of Fe and an unavoidable impurity composition, wound up to 750 ° C or lower, and thereafter 750 ° C or higher After heating by heating to cool, the thickness of the band-like structure composed of the second phase is T _b / T

A method for producing a high strength steel sheet having excellent workability and plating property, characterized in that it is adjusted to a range of 0.005 (T _b : average thickness in the thickness direction of the band-like structure, T: steel sheet thickness).

0.005 (단, T_b : 밴드형 조직의 판두께 방향 평균두께, T : 강판 두께) 범위로 조정하는 것을 특징으로 하는 가공성 및 도금성이 우수한 고강도 박강판의 제조방법.(4) In (3), after winding up to 750 ° C. or lower, cold rolling is performed, and after heating to 750 ° C. or higher, the thickness of the band structure composed of the second phase is reduced by T _b / T.

A method for producing a high strength steel sheet having excellent workability and plating property, characterized in that it is adjusted to a range of 0.005 (T _b : average thickness in the thickness direction of the band-like structure, T: steel sheet thickness).

(5) Processability and plating property in (3) or (4) which are heated to the above 750 ° C and then hot-dip galvanized during cooling or by heat alloying after hot-dip galvanizing. Excellent high strength steel sheet manufacturing method.

0.005 (단, T_b : 밴드형 조직의 판두께 방향 평균두께, T : 강판 두께) 범위로 조정하고, 그 후에 다시 700 ∼ 850 ℃ 로 가열하고, 그 후에 냉각 도중에 용융아연도금을 하거나 용융아연도금한 후에 다시 가열 합금화 처리하는 것을 특징으로 하는 가공성 및 도금성이 우수한 고강도 박강판의 제조방법.(6) In (3) or (4), the thickness of the band-like structure composed of the second phase is reduced by heating to the aforementioned 750 ° C. or higher and then T _b / T.

0.005 adjustment (where, T _b:: band-average thickness in the sheet thickness direction, of the tissue T steel plate thickness) range, and thereafter again heated to 700 ~ 850 ℃, and thereafter hot-dip galvanizing during a cooling or hot-dip galvanized The method of producing a high strength steel sheet having excellent workability and plating property after the heat alloying treatment.

(7) The method for producing a high strength steel sheet having excellent workability and plating property according to (5) or (6), wherein the plating adhesion amount of the hot dip galvanizing is 20 to 120 g / m 2 as the adhesion amount per sheet.

(8) The workability and plating property according to any one of (5) to (7), wherein the plating adhesion amount of the alloyed hot dip galvanization after the heat alloying treatment is 20 to 120 g / m 2 as an adhesion amount per sheet steel sheet. Excellent high strength steel sheet manufacturing method.

(9) The slab according to any one of (3) to (8), further comprising one or two or more selected from Nb: 1.0 wt% or less, Ti: 1.0 wt% or less, V: 1.0 wt% or less. A manufacturing method of high strength steel sheet excellent in workability and plating property, characterized by containing.

(10) The one or two of (3) to (8), wherein the slab is further selected from Nb: 0.001-1.0 wt%, Ti: 0.001-1.0 wt%, and V: 0.001-1.0 wt%. A method for producing a high strength steel sheet having excellent workability and plating property, comprising species or more.

(11) In (3), after winding up to 750 ° C. or lower, pickling is carried out, and thereafter, in an annealing furnace, 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, still more preferably 800 ° C. or higher, After heating and cooling to 1000 DEG C or lower, the concentrated layer of the steel component on the surface of the steel sheet is removed by pickling, followed by heat reduction under reducing conditions of the P-based oxide, which is a pickling residue on the surface of the steel sheet, followed by hot dip galvanizing. Process for producing high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, characterized in that.

(12) In (3), after winding at 750 ° C. or lower, pickling is carried out, and then cold rolling is performed, and then 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, further preferably in an annealing furnace. Preferably, after heating and cooling to 800 degreeC or more and 1000 degrees C or less, the concentrated layer of the steel component of the steel plate surface is removed by pickling, and it heat-reduces under the reducing conditions of the P-type oxide which is the pickling residue of the steel plate surface, and Process for producing high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, characterized in that the hot dip galvanizing.

(13) After winding at 750 ° C. or lower in (3) above, pickling is carried out, and then in an annealing furnace, 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, still more preferably 800 ° C. or higher, and 1000 After heating to below the temperature and cooling, the concentrated layer of the steel component on the surface of the steel sheet is removed by pickling, and then the dew point of the atmosphere gas: -50 ° C to 0 ° C, and the hydrogen concentration of the atmosphere gas: 1 to 100 vol%. Process for producing a high strength hot dip galvanized steel sheet excellent in workability and plating adhesion characterized by hot-dip galvanizing after heat reduction.

(14) After winding at 750 ° C. or lower in (3) above, pickling is carried out, followed by cold rolling, and then 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, more preferably in an annealing furnace. After heating and cooling to 800 degreeC or more and 1000 degrees C or less, the concentrated layer of the steel component of the steel plate surface is removed by pickling, and then dew point of atmospheric gas: -50 degreeC-0 degreeC, hydrogen concentration of atmospheric gas: 1 A method of producing a high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, characterized by performing hot dip galvanizing after heating under a 100 vol% condition.

(15) After winding up at 750 ° C. or lower in (3), pickling is carried out, and thereafter, in an annealing furnace, 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, still more preferably 800 ° C. or higher, and 1000 After heating to below the temperature and cooling, the concentrated layer of the steel component on the surface of the steel sheet was removed by pickling, and then the heating reduction temperature: t ₁ (° C.) was represented by the following formula (1) for the P content in the steel: P (wt%). A method for producing a high strength hot dip galvanized steel sheet having excellent workability and plating adhesion, characterized by performing hot dip galvanizing after heat reduction under conditions satisfying the above conditions.

{[P(wt%) + (2/3)] ×1100}/{t₁(℃)}

1.1 …(1)0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C)}

1.1... (One)

(16) After winding up at 750 ° C. or lower in (3) above, pickling is carried out, followed by cold rolling, and then 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, more preferably in an annealing furnace. is then heated in a range from 800 ℃, 1000 ℃, it cooled, removing the concentrated layer of steel components in the steel sheet surface by pickling, then heating-reduction temperature: the t ₁ (℃) steel P content: P (wt%) A method of producing a high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, characterized by performing hot dip galvanizing after heat reduction under conditions satisfying the following formula (1).

{[P(wt%)+(2/3)]×1100}/{t₁ (℃)}

1.1 …(1)0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}

1.1... (One)

(17) After winding up at 750 ° C. or lower in (3), pickling is carried out, and then in an annealing furnace, 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, still more preferably 800 ° C. or higher, and 1000 After heating to below the temperature and cooling, the concentrated layer of the steel component on the surface of the steel sheet is removed by pickling, and then the dew point of the atmosphere gas: -50 ° C to 0 ° C, the hydrogen concentration of the atmosphere gas: 1 to 100 vol%, heating Reduction temperature: t ₁ (° C.) is heat reduced under conditions satisfying the following formula (1) with respect to P content in steel: P (wt%), followed by hot dip galvanizing, and is excellent in workability and plating adhesion. Method for producing high strength hot dip galvanized steel sheet.

{[P(wt%)+(2/3)]×1100}/{t₁ (℃)}

1.1 …(1)0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}

1.1... (One)

(18) After winding at 750 ° C. or lower in (3) above, pickling is carried out, followed by cold rolling, and then 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, more preferably in an annealing furnace. After heating and cooling to 800 degreeC or more and 1000 degrees C or less, the concentrated layer of the steel component of the steel plate surface is removed by pickling, and then dew point of atmospheric gas: -50 degreeC-0 degreeC, hydrogen concentration of atmospheric gas: 1 ~ 100 vol%, heat reduction temperature: t ₁ (° C.) is subjected to heat reduction under conditions satisfying the following formula (1) for P content in the steel: P (wt%), followed by hot dip galvanizing. Process for producing high strength hot dip galvanized steel sheet with excellent workability and plating adhesion.

{[P(wt%)+(2/3)]×1100}/{t₁ (℃)}

1.1 …(1)0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}

1.1... (One)

1, 액온 : 40 ∼ 90 ℃ 의 산세척액 중에서 1 ∼ 20 초간 산세척하는 산세척법인 것을 특징으로 하는 가공성 및 도금 밀착성이 우수한 고강도 용융아연도금 강판의 제조방법.(19) The heating method according to any one of (11) to (18), wherein the annealing furnace is heated to 750 ° C or higher, more preferably 750 ° C or higher, 1000 ° C or lower, still more preferably 800 ° C or higher and 1000 ° C or lower. After cooling and cooling, the pickling method

1, Liquid temperature: It is an pickling method for pickling for 1 to 20 seconds in a pickling solution at 40 to 90 ℃, characterized in that the workability and plating adhesion excellent manufacturing method of high strength hot-dip galvanized steel sheet.

(20) The heating method according to any one of (11) to (19), wherein the annealing furnace is heated to 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, still more preferably 800 ° C. or higher and 1000 ° C. or lower. After cooling, the pickling liquid is HCl concentration: 1 to 10 wt% hydrochloric acid solution, characterized in that the workability and plating adhesion excellent manufacturing method of high strength hot-dip galvanized steel sheet.

(21) After picking up at 750 ° C. or lower in (3) and pickling, the heating temperature: T satisfies the following formula (2) at 750 ° C. or higher and 1000 ° C. or lower, and the dew point of the atmospheric gas: t A method for producing a high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, which satisfies the following formula (3) and is heated in an atmosphere having a hydrogen concentration of 1 to 100 vol%, followed by hot dip galvanizing.

{[P(wt%)+(2/3)]×1150}/{T(℃)}

1.15 …(2)0.85

{[P (wt%) + (2/3)] × 1150} / {T (° C)}

1.15. (2)

{[P(wt%)+(2/3)]×(-30)}/{t(℃)}

1.8 …(3)0.35

{[P (wt%) + (2/3)] × (-30)} / {t (° C)}

1.8... (3)

(22) After picking up at 750 ° C. or lower in (3), pickling and then cold rolling, heating temperature: T satisfies the following formula (2) at 750 ° C. or higher and 1000 ° C. or lower. Dew point of gas: Preparation of high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, characterized in that t satisfies the following formula (3) and is heated in an atmosphere having a hydrogen concentration of 1 to 100 vol%, followed by hot dip galvanizing. Way.

{[P(wt%)+(2/3)]×1150}/{T(℃)}

1.15 …(2)0.85

{[P (wt%) + (2/3)] × 1150} / {T (° C)}

1.15. (2)

{[P(wt%)+(2/3)]×(-30)}/{t(℃)}

1.8 …(3)0.35

{[P (wt%) + (2/3)] × (-30)} / {t (° C)}

1.8... (3)

(23) The slab according to any one of (11) to (22), further comprising one or two or more selected from Nb: 1.0 wt% or less, Ti: 1.0 wt% or less, V: 1.0 wt% or less. A method for producing a high strength hot-dip galvanized steel sheet having excellent workability and plating adhesion, characterized by containing.

(24) The one or two of (11) to (22), wherein the slab is further selected from Nb: 0.001-1.0 wt%, Ti: 0.001-1.0 wt%, and V: 0.001-1.0 wt%. A method for producing a high strength hot-dip galvanized steel sheet excellent in processability and plating adhesion, characterized by containing more than one species.

(25) The high strength excellent in workability and plating adhesion as described in any one of (11) to (24), wherein the plating adhesion amount of the high strength hot-dip galvanized steel sheet is 20 to 120 g / m 2 as the adhesion amount per sheet. Method for producing hot dip galvanized steel sheet.

(26) When any one of (13), (14), (17), (18), (21) and (22) has a hydrogen concentration of the above-described atmosphere gas of 1 vol% or more and less than 100 vol% Process for producing high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, characterized in that the residual gas is an inert gas.

(27) The method for producing a high strength hot dip galvanized steel sheet excellent in processability and plating adhesion, wherein inert gas is nitrogen gas in (26).

(28) The hot-dip galvanized steel sheet obtained by the method for producing a high-strength hot-dip galvanized steel sheet according to any one of (11) to (27) is further subjected to heat alloying treatment. Method for producing hot dip galvanized steel sheet.

(29) The hot dip galvanized steel sheet obtained by the method for producing a high strength hot dip galvanized steel sheet according to any one of (11) to (27) was further subjected to a heat alloying treatment and the alloying temperature in the heat alloying treatment: t Processability and plating adhesion characterized by satisfying the following formula (4) for P content in the steel at ₂ ° C .: P (wt%) and Al content in the bath during hot dip galvanizing: Al (wt%). Excellent high strength alloyed hot dip galvanized steel sheet production method.

[7×{100×P(wt%)+(2/3)]+ 10×Al(wt%)}]/[t₂ (℃)]

1.05 …(4)0.95

[7 × {100 × P (wt%) + (2/3)] + 10 × Al (wt%)}] / [t ₂ (° C.)]

1.05... (4)

(30) The slab according to (28) or (29) further contains one or two or more selected from Nb: 1.0 wt% or less, Ti: 1.0 wt% or less, V: 1.0 wt% or less. Process for producing high strength alloyed hot dip galvanized steel sheet excellent in workability and plating adhesion.

(31) In (28) or (29), the slab further contains one or two or more selected from Nb: 0.001-1.0 wt%, Ti: 0.001-1.0 wt%, and V: 0.001-1.0 wt%. A method for producing a high strength alloyed hot dip galvanized steel sheet having excellent workability and plating adhesion.

(32) The workability according to any one of (28) to (31), wherein the plating adhesion amount of the alloyed hot dip galvanizing of the high strength alloyed hot dip galvanized steel sheet is 20 to 120 g / m 2 as an adhesion amount per sheet of steel sheet. And a high strength alloyed hot dip galvanized steel sheet having excellent plating adhesion.

(33) An alloyed hot dip galvanized steel sheet obtained by hot-dip galvanizing a steel sheet containing 1.00 wt% or less of Mo, wherein the Fe content in the alloyed hot dip galvanized layer is 8-11 wt% and the Mo content is 0.002-0.11. A high strength alloyed hot dip galvanized steel sheet having excellent workability, plating adhesion and corrosion resistance, characterized in that it is wt%.

(34) An alloyed hot dip galvanized steel sheet obtained by hot-dip galvanizing a steel sheet containing 1.00 wt% or less of Mo and 0.010 to 0.2 wt% of C, and having a Fe content of 8% in the alloyed hot dip galvanized layer. -11 wt%, Mo content is 0.002 to 0.11 wt%, high strength alloyed hot-dip galvanized steel sheet excellent in workability, plating adhesion and corrosion resistance.

(35) The workability according to (33) or (34), wherein the steel sheet containing 1.00 wt% or less of Mo is a steel sheet containing 0.01 to 1.00 wt%, more preferably 0.05 to 1.00 wt% of Mo. High strength alloyed hot dip galvanized steel with excellent plating adhesion and corrosion resistance.

(36) The base material steel sheet as described in any one of (33) to (35), wherein Si is 1.0 wt% or less, Mn: 1.0 to 3.0 wt%, P: 0.10 wt% or less, S: 0.05 Processability, plating adhesion, and the like, characterized in that the steel sheet contains wt% or less, Al: 0.10 wt% or less, N: 0.010 wt% or less, Cr: 1.0 wt% or less, and the remaining portion is composed of Fe and inevitable impurities. High strength alloyed hot dip galvanized steel sheet with excellent corrosion resistance.

(37) The base steel sheet according to any one of (33) to (36), wherein the base steel sheet is one selected from Nb: 1.0 wt% or less, Ti: 1.0 wt% or less, V: 1.0 wt% or less, or A high strength alloyed hot dip galvanized steel sheet excellent in workability, plating adhesion and corrosion resistance, containing two or more kinds.

(38) The base material steel sheet as described in any one of (33) to (36) is further selected from Nb: 0.001-1.0 wt%, Ti: 0.001-1.0 wt%, and V: 0.001-1.0 wt%. A high strength alloyed hot dip galvanized steel sheet excellent in workability, plating adhesion and corrosion resistance, characterized by containing one or two or more kinds.

(39) The workability according to any one of (33) to (38), wherein the plating adhesion amount of the alloyed hot dip galvanizing of the high strength alloyed hot dip galvanized steel sheet is 20 to 120 g / m 2 as an adhesion amount per sheet of steel sheet. High strength alloyed hot dip galvanized steel with excellent plating adhesion and corrosion resistance.

Best Mode for Carrying Out the Invention

First, the experimental results that are the basis of the present invention for improving mechanical properties will be described.

0.09 wt% C-0.01 wt% Si-2.0 wt% Mn-0.009 wt% P-0.003 wt% S-0.041 wt% Al-0.0026 wt% N-0.15 wt% Mo-0.02 wt% Cr, with the remainder substantially Fe A sheet bar having a thickness of 30 mm was heated to 1200 ° C. in a chemical composition consisting of a hot rolled steel sheet having a thickness of 2.5 mm in five passes, wound at 640 ° C., pickled, and heated at 750 ° C. to 900 ° C. for 1 minute. Hold (1 time heating) and cool to room temperature at 10 ° C / sec cooling rate.

Subsequently, heating was maintained at 750 ° C. for 1 minute (2 times heating), cooled to 500 ° C. at 10 ° C./sec cooling rate and maintained for 30 sec, and then heated to 550 ° C. at 10 ° C./sec heating rate and maintained at 20 sec. Cool to room temperature immediately at a cooling rate of 10 ° C / sec.

The relationship between TS, YR, TS x El of the obtained steel sheet, and the thickness of the band structure in the cross section of the steel sheet thickness direction after the first heating was examined to obtain the result shown in FIG.

In addition, the thickness of the band structure is represented by T _b / T (wherein T _b : plate thickness direction of the band structure consisting of the second phase, T: steel sheet thickness).

However, T _b is the average value obtained by measuring thickness of all band-like tissue in the plate thickness direction at the magnification of 1500 times the image to an image analysis device.

It is also less than T _b / T of the steel sheet after the first round from the first heating of 0.005, was found to have good also in low yield ratio TS × E1 balance.

That is, when Mn is added in a large amount for the purpose of securing strength as in the present invention, a band-like structure composed mainly of a second phase composed of cementite, pearlite and bainite having a sufficient amount of C and Mn is well developed.

In this case, prior to heating (second time heating) of the continuous hot-dip galvanizing line (CGL), by heating once at a predetermined temperature with a facility such as a continuous annealing line, the thickness of the band structure is made thin and finely dispersed. Even when the band-like structure is dissolved during heating of the hot-dip galvanizing line and maintained during the plating process or the heat alloying process, the martensite is properly dispersed in the ferrite substrate after cooling, thereby achieving good workability and high strength. You can do it.

It is a phenomenon that can occur even when high temperature heating is performed in a continuous hot dip galvanizing line, and there is no change in material by only one heating of the continuous hot dip galvanizing line.

However, high-temperature heating is likely to be poor in Mn plating on the surface of the steel sheet, and inferior plating performance.To ensure more stable plating, heating once in a continuous annealing line and heating twice in a continuous hot dip galvanizing line is recommended. More preferred.

The dispersion effect of the band-like tissue by the one-time heating can be seen in the comparison of the microscopic tissues shown in FIGS. 2 and 3.

Here, FIG. 2A shows the metal structure before 1st heating, and FIG. 2B is a schematic diagram of FIG. 2A.

3A shows the metal structure after the first heating, and FIG. 3B is a schematic diagram of FIG. 3A.

2B and 3B, B.S. Denotes a band-like structure consisting mainly of cementite, pearlite, bainite and a second phase in which only a few are martensite, residual austenite.

In the tissue before the first heating shown in FIG. 2, the T _b / T value is 0.0070 on average, whereas in the tissue after the first heating shown in FIG. 3, band-shaped tissue dispersion is achieved, thereby reducing T _b / T to 0.0016 on the average.

Next, the present invention for further improving the plating property will be described in detail.

The present inventors further examined the composition, annealing conditions, and alloying conditions of the base steel sheet necessary for preventing defects of the plating, and improving the workability and plating adhesion. As a result, the present inventors obtained the following knowledge (1) to (3). Leads to

(1) two-stage heating and pickling method:

After heating and cooling a steel sheet having a predetermined composition to 750 ° C. or higher, more preferably 800 ° C. or higher in an annealing furnace, the concentrated layer of the steel component on the surface of the steel sheet is removed by pickling, and then again in a continuous hot dip galvanizing line. After annealing the steel sheet at an appropriate heat reduction temperature in a predetermined reducing atmosphere, it has been found that high-strength hot-dip galvanized steel sheet can be obtained by preventing hot-dip galvanizing to prevent plating defects and excellent plating adhesion and corrosion resistance.

In addition, the above-mentioned treatment method before hot dip galvanizing (: annealing furnace heating → pickling → heating reduction) is also called a two-stage heating and pickling treatment method.

(2) one-stage heating treatment method:

As a result of further studies, it is possible to obtain a good plating property and plating adhesion in one-step heating by heating a steel plate having a predetermined composition in a hydrogen-containing gas having a suitable heating temperature and a suitable dew point, and then performing hot dip galvanizing. It turned out.

In addition, the above-mentioned heat processing method (hot reduction) before hot dip galvanizing is also called single-stage heat processing method.

(3) alloying treatment method:

The hot-dip galvanized steel sheet obtained in the above (1) and (2) is preferably alloyed under a condition that satisfies a predetermined alloying temperature, whereby a high-strength alloyed hot-dip galvanized steel sheet having excellent plating adhesion and corrosion resistance after alloying can be obtained. It turned out.

Next, the experiment which became the basis of this invention for improving said plating property is demonstrated.

[2 stage heating and pickling treatment method]

0.09 wt% C-0.01 wt% Si-2.0 wt% Mn-0.005-0.1 wt% P-0.003 wt% S-0.041 wt% Al-0.0026 wt% N-0.15 wt% Mo-0.02 wt% Cr, residual part substantially By heating the sheet bar having a thickness of 30 mm to 1200 ℃ by a chemical composition consisting of Fe to obtain a hot rolled steel sheet having a thickness of 2.5 mm in five passes.

Next, the obtained hot rolled steel sheet is treated in the following order (1) to (10).

(1) Heat-treat at 540 degreeC for 30 minutes, and perform a winding correspondence process.

(2) Liquid temperature: Pickling for 40 seconds in a 5 wt% HCl solution at 80 ℃.

(3) Hold | maintain for 1 minute at 800 degreeC (steel plate temperature) in the reducing atmosphere containing hydrogen in an annealing furnace.

(4) Cool to room temperature at 10 ° C / sec cooling rate.

(5) Solution temperature: Pickling for 10 seconds in a 5 wt% HCl solution at 60 ℃.

(6) Hold | maintained for 20 second at 650-950 degreeC (steel plate temperature) in reducing atmosphere containing hydrogen.

(7) Cool down to 480 ° C at 10 ° C / sec cooling rate.

(8) Bath temperature containing 0.15 wt% of Al: Hot dip galvanized by immersion for 1 second in hot dip galvanizing bath at 480 ° C.

(9) The plating adhesion amount of the plated steel plate pulled up from the hot dip galvanizing bath was adjusted to 50 g / m 2 by gas wiping.

(10) For a hot-dip galvanized steel sheet obtained by hot-dip galvanizing under the above conditions immediately after heat reduction under the conditions of H ₂ concentration: 7 vol%, dew point (: dp): -25 ° C, and steel sheet temperature: 800 ° C, The heat alloying process is performed at 450-600 degreeC.

Next, the performance of the obtained plated steel sheet is evaluated by the following evaluation method and evaluation criteria.

[Platability]

The appearance of the plated steel sheet (non-alloyed hot dip galvanized steel sheet) after hot dip galvanizing was visually evaluated.

: 도금이 안되는 결함이 전혀 없음 (도금성 양호)

: No plating defects (good plating)

X: defect generation which cannot be plated

[Plating adhesion]

After bending the plated steel sheet 90 degrees, the compression-side plating layer was peeled off the cellophane tape and evaluated by the amount of the plating film attached to the cellophane tape.

(Unalloyed Plated Steel Sheet)

: 도금층의 박리 없음 (도금 밀착성 양호)

: No peeling off of plating layer (good plating adhesion)

X: There is peeling of the plating layer (poor adhesion)

(Coated Steel Plate)

: 도금 박리량이 적음 (도금 밀착성 양호)

: Low plating peeling amount (good plating adhesion)

X: large amount of plating peeling (poor adhesion)

[Appearance after alloying]

Evaluate visually.

: 합금화 편차가 없어 균일한 외관을 얻을 수 있음

: There is no deviation of alloying to get a uniform appearance

×: alloying deviation occurs

4 and 5 show the evaluation results of the plating property of the hot-dip galvanized steel sheet, and FIG. 6 shows the evaluation results of the plating adhesion of the alloyed hot-dip galvanized steel sheet.

As shown in Figs. 4 and 5, in order to ensure good plating property, dew point, hydrogen concentration, and steel sheet of atmospheric gas in the heat reduction (heat reduction after annealing furnace and then pickling) during hot dip galvanizing It has been found that the P-based oxide determined at the heating temperature can secure a good plating property under the thermodynamically reduced conditions.

Heat-reducing temperature (steel sheet temperature) of the present invention range in a reduction in heating Figure 4: t ₁ (℃) is expressed by the following formula (1).

{[P(wt%)+(2/3)]×1100}/{t₁ (℃)}

1.1 …(1)0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}

1.1... (One)

In addition, P (wt%) in said Formula (1) shows P content in steel.

And when alloying a hot-dip galvanized steel sheet, it turned out that it is necessary to satisfy the alloying temperature (steel plate temperature) of the range of this invention shown in FIG. 6 in order to ensure favorable plating adhesiveness.

Alloying temperature (steel sheet temperature) of the present invention range in FIG. 6: t ₂ (℃) is expressed by the following formula (4).

[7×{100×[P(wt%)+(2/3)]+ 10 ×Al(wt%)}]/[t₂ (℃)]

1.05 …(4)0.95

[7 × {100 × [P (wt%) + (2/3)] + 10 × Al (wt%)}] / [t ₂ (° C.)]

1.05... (4)

In the formula (4), P (wt%) represents P content in steel, and Al (wt%) represents Al content in a bath during hot dip galvanizing.

That is, the present inventors annealing in an annealing furnace as a method for improving the plating property of a steel sheet having a high content of dioxide elements such as Mn such as a high tensile strength steel sheet, and depositing a surface concentrate of dioxide elements such as Mn on the surface of the steel sheet. After removal of the concentrate by washing, hot dip galvanizing is performed immediately after heating and reducing the P-based oxide, which is determined at the dew point of the atmospheric gas, the hydrogen concentration, and the steel sheet heating temperature, in a thermodynamically suitable atmosphere gas condition. It has been found that a high strength hot dip galvanized steel sheet can be produced without generation.

In the case of alloying treatment after hot dip galvanizing, when the alloying treatment is performed according to the P content in the steel and the Al content in the bath during hot dip galvanizing, a high strength alloyed hot dip galvanized steel sheet having good plating adhesion after alloying can be produced. It was found that it can.

On the other hand, the inventors of the present invention, the alloyed hot-dip galvanized steel sheet having a steel of the same composition as the hot rolled steel sheet used in the experiment of the two-stage heating and pickling treatment method described above, 10 wt% Fe content in the plating layer after alloying, in the plating layer An alloyed hot-dip galvanized steel sheet based on a plated steel sheet having a Mo content of 0.01 wt% and a steel having no composition only as a base, and having a Fe content of 10 wt% in the plating layer after alloying and a 0 wt% Mo content in the plating layer. Start the steel sheet.

7 shows the results of the SST test (saline spray test) of the obtained alloyed hot-dip galvanized steel sheet.

As shown in FIG. 7, it can be seen that the alloying hot-dip galvanized steel sheet containing Mo has a low corrosion loss and can significantly improve the corrosion resistance of the alloyed hot-dip galvanized steel sheet containing no Mo.

[1 step heat treatment method]

The present inventors further experimented in the same manner as described above for the purpose of simplifying the process consisting of the above two stages of heat treatment and pickling carried out between these heat treatments.

As a result, after hot-rolling and pickling the steel slab of the predetermined structure, and after or as it is cold-rolled, the heating temperature: T in the annealing furnace satisfies the following formula (2) at 750 ° C or more and 1000 ° C or less Dew point of gas: t meets the following formula (3) and is heated in an atmosphere of hydrogen concentration of 1 to 100 vol%, followed by hot dip galvanizing, thereby heating in one step with or without Mo addition and hot dip zinc. It has been found that a high-strength hot-dip galvanized steel sheet excellent in plating properties and plating adhesion can be produced without pickling in a plating line.

{[P(wt%)+(2/3)]×1150}/{T (℃)}

1.15 …(2)0.85

{[P (wt%) + (2/3)] × 1150} / {T (° C)}

1.15. (2)

{[P(wt%)+(2/3)]×(-30)}/{t(℃)}

1.8 …(3)0.35

{[P (wt%) + (2/3)] × (-30)} / {t (° C)}

1.8... (3)

8, a steel sheet obtained by hot-dip galvanizing on heating under H ₂ -N ₂ atmosphere the Mo-free steel in Figure 9 without annealing, pickling and then cold rolling for cold-rolled steel sheet as the base material in a hot-dip galvanizing line In this case, the evaluation result of the plating property of the hot-dip galvanized steel sheet is shown.

As shown in Fig. 8 and Fig. 9, the steel sheet was heated under the hydrogen-containing gas condition in which the heating temperature: T and the dew point of the atmosphere gas: t were precisely controlled before the hot dip galvanizing process, and thus the presence or absence of Mo addition was observed. It was found that a high-strength hot-dip galvanized steel sheet excellent in plating property and plating adhesion can be produced regardless of the one-step heating and pickling in the hot-dip galvanizing line.

In FIG. 8, the heating temperature (steel plate temperature): T (degreeC) of the range of this invention at the time of the heating of the whole process of hot dip galvanizing becomes the following range.

0.072 wt% 의 경우:P (wt%)

For 0.072 wt%:

{[P(wt%)+(2/3)]×1150}/{T(℃)} 0.85

{[P (wt%) + (2/3)] × 1150} / {T (° C)}

T (℃)And 750 ℃

T (℃)

P(wt%)

0.083 wt% 의 경우:0.072 wt%

P (wt%)

For 0.083 wt%:

T (℃)

1000 ℃750 ℃

T (℃)

1000 ℃

P(wt%)

0.10 wt% 의 경우:0.083 wt%

P (wt%)

For 0.10 wt%:

1.15 {[P (wt%) + (2/3)] × 1150} / {T (° C)}

1.15

T (℃)And 1000 ℃

T (℃)

In Fig. 9, the dew point: t (° C) of the atmospheric gas in the range of the present invention during the heating of the hot dip galvanizing step is in the following range.

{[P(wt%)+(2/3)]×(-30)}/{t(℃)}

1.80.35

{[P (wt%) + (2/3)] × (-30)} / {t (° C)}

1.8

Hereinafter, the reason for defining the composition of the base steel sheet and the manufacturing conditions of the base metal sheet in the present invention will be described.

I. Composition of the base steel sheet:

C: 0.01-0.20 wt%

C is one of the important basic constituents of steel, and in the present invention, it is an important element because it affects the volume fraction of the γ phase and further, the amount of martensite after cooling, when heated to (α + γ). And mechanical properties such as strength greatly depend on the martensite fraction and the hardness of the martensite phase. If the amount of C is less than 0.01 wt%, the martensite phase is hardly formed, whereas if the amount of C is less than 0.20 wt%, the spot weldability deteriorates, so the range is set to 0.01 to 0.20 wt%. Moreover, more preferable amount of C is 0.03-0.15 wt%.

Si: 1.0 wt% or less

Si is an element which improves workability such as elongation by decreasing the amount of solid solution C in the α phase, but the content of Si in excess of 1.0 wt% impairs spot weldability and plating property, so the upper limit is 1.0 wt%. Moreover, more preferable Si amount is 0.5 wt% or less.

Mn: 1.0-3.0 wt%

In the present invention, Mn has an effect of thickening to a γ phase and promoting martensite transformation, and is an important element as a basic component. However, the addition of less than 1.0 wt% does not have an effect, whereas if it exceeds 3.0 wt%, the spot weldability and plating properties are remarkably impaired, so Mn is added in the range of 1.0 to 3.0 wt%, more preferably 1.5 to 2.5 wt%. do.

P: 0.10 wt% or less

Although P is an effective and inexpensive element for obtaining a high strength steel sheet, since the spot weldability is remarkably lost when the content exceeds 0.10 wt%, the P content of the base steel sheet is defined to be 0.10 wt% or less. In this invention, it is more preferable to make P content of a base material steel plate into 0.005-0.05 wt%.

S: 0.05 wt% or less

S is not only a basis for causing hot cracking during hot rolling, but also causes breakage in the nugget of the spot welded portion, and therefore it is desirable to reduce the strength as much as possible. Therefore, in this invention, S content of a base material steel plate shall be 0.05 wt% or less. In addition, the amount of S is more preferably limited to 0.010 wt% or less.

Al: 0.10 wt% or less

Al is an effective element which fixes N as AlN which causes aging deterioration as a deoxidizer in a steelmaking process. However, containing in excess of 0.10 wt% leads to an increase in manufacturing cost, so the Al content should be suppressed to 0.10 wt% or less. Moreover, more preferable amount of Al is 0.050 wt% or less.

N: 0.010 wt% or less

In addition to causing aging deterioration, N causes an increase in yield point (yield ratio) and generation of yield elongation. Therefore, N should be suppressed to 0.010 wt% or less. Moreover, more preferable N amount is 0.0050 wt% or less.

Cr: 1.0 wt% or less

Cr is an element that is effective for obtaining a composite structure of ferrite + martensite similarly to Mn and Mo. However, Cr is not more than 1.0 wt% because addition of more than 1.0 wt% impairs plating properties. Moreover, more preferable content of Cr is 0.5 wt% or less.

Mo: 0.001-1.00 wt%

Mo, like Mn, is an effective element for achieving a solid solution by obtaining a composite structure of ferrite + martensite without impairing the plating property.

In addition, according to the present invention, the Mo-added steel was found to have a better reducing ability of the P-based pickling residue (: P-based oxide) than that of the Mo-added steel, resulting in an improvement in plating adhesion.

The details of the cause are not clear, but Mo is added to P to form a condensation acid, and Mo is incorporated into the P-based oxide in some form to reduce the oxygen potential felt by the dissolved residue. It is speculated that the reduction of pickling residues is encouraged and consequently the plating adhesion is improved.

Moreover, when the base material steel plate which added Mo was used, the corrosion resistance of the plated steel plate obtained tends to become favorable. Mo is an element harder to oxidize than Fe, and it can be seen that a slight diffusion and addition of Mo to the plating layer improves the corrosion resistance. In this invention, in order to acquire the said effect, Mo content in a base material steel plate is prescribed | regulated to 0.001 wt% or more. However, additions exceeding 1.00 wt% are specified to be 1.00 wt% or less because they significantly increase the manufacturing cost. In this invention, it is more preferable to make Mo content of a base material steel plate into 0.01-1.00 wt%, and it is still more preferable to set it as 0.05-1.00 wt%. Moreover, Mo content of the most preferable base material steel plate of this invention is 0.05-0.5 wt%.

Ti: 0.001-1.0 wt%, Nb: 0.001-1.0 wt%, V: 0.001-1.0 wt%

Ti, Nb and V are effective elements for forming carbides and strengthening the steel, and it is preferable to add 0.001 wt% or more, if necessary. However, if any element is added in excess of 1.0 wt%, the yield point (yield ratio) is raised in addition to the disadvantage of an increase in cost, thereby degrading workability. Therefore, when adding these elements, all these elements are added in 0.001-1.0 wt%. In addition, these elements are preferably 0.001 to 1.0 wt% in the total amount added.

Ⅱ. Manufacturing conditions

Subsequently, II.-1: High-strength thin steel plate which prescribes thickness of band-like structure of this invention, II.-2: Two stage heating and pickling treatment method, II.-3: One stage heating treatment method, II.-4: The manufacturing conditions of the hot dip galvanizing and the heat alloying treatment method will be described in order.

Ⅱ.-1: Manufacturing conditions of high strength steel sheet specifying the thickness of band structure:

In the present invention, the steel slab composed of the above-described component composition is hot rolled and wound at 750 ° C. according to a conventional method.

The reason why the coiling temperature is 750 ° C. or lower is that if the coiling temperature is exceeded, the scaling thickness becomes thick and the pickling efficiency is deteriorated. In addition, the edge part and the center part of the coil length direction, the center part, the rear end part or the coil width direction This is because the cooling rate is greatly different after winding in between, resulting in a large material variation. Moreover, more preferable winding temperature is 700 degrees C or less. In addition, when the coiling temperature is lowered to an excessive temperature, it is preferable that the deterioration of the cold rolling property occurs well so as not to fall below 300 ° C.

Subsequently, the hot rolled steel sheet obtained above is pickled and descaled, and if necessary, cold rolled again, and then heated to 750 ° C. or higher to form a mother plate for galvanizing.

According to the present invention, after plating at a temperature range of 750 DEG C or more (continuous annealing line is suitable), the concentrated structure of C and Mn is dissolved, dispersed and cooled in a band-like structure, and then the ferrite + martensite complex structure is efficiently removed. To improve workability.

That is, in the case where the Mn content is large, as in the present invention, a band-like structure mainly composed of cementite, pearlite, and bainite tends to be formed, and therefore, adverse effects should be eliminated.

0.005 로서 밴드형 조직의 두께를 그 범위까지 얇게 하고 잘게 분산시켜 두면 연속 용융아연도금 라인에서의 가열중에 밴드형 조직을 용해시키고 도금 과정 혹은 추가로 가열 합금화 처리과정에서 유지된 경우라도 냉각한 후 페라이트 소지중에 마르텐사이트상을 적합하게 분산시켜 양호한 가공성과 고강도를 양립시킬 수 있게 된다.In addition, the relationship between the average thickness (Tb) and the plate thickness (T) of the band-like structure (Tb / T)

If the thickness of the band-like tissue is thinned and finely dispersed to the extent as 0.005, the band-like tissue is dissolved during heating in the continuous hot dip galvanizing line and then cooled after ferrite even if maintained in the plating process or further heat alloying process. The martensite phase is suitably dispersed in the substrate to achieve good processability and high strength.

The dispersion effect of the band-like structure according to the heating (single-time heating) before such plating is as shown in Figs.

Further, pickling and descaling between the winding after hot rolling and the first heating does not affect the effect of the present invention.

In the case where the plated mother plate thus prepared is plated to form a thin steel sheet, the pickling treatment may be performed prior to the galvanizing after the above-described first heating.

The pickling is carried out to remove surface concentrated layers such as Mn, Cr, etc. generated during the heating to improve more stable plating property.

Further, temper rolling may be performed between the first heating and the pickling process in order to improve the flowability of the plating line, which is a post-process.

Subsequently, hot dip galvanizing or electroplating is performed.

In the case of hot-dip galvanizing, re-heating is performed at the hot dip galvanizing line (CGL) at 700 ° C. or higher (1 time heating or 2 times heating) before plating.

If the heating temperature before plating is 700 degrees C or less, the surface of a steel plate will not be reduced and a plating plating defect will be caused well, a desired structure and material cannot be obtained, and it heats at 700 degreeC or more.

Moreover, as for the heating temperature at the time of reheating before plating, 750-900 degreeC temperature is more preferable.

In the present invention, the alloying treatment may be continued after hot dip galvanizing.

In addition, instead of hot dip galvanizing, electrogalvanization may be performed, and in this case, an effect equivalent to hot dip galvanizing may be obtained.

II.-2: Manufacturing conditions in the case of the two-stage heating and pickling treatment method (: annealing furnace heating → acid washing → heat reduction → hot dip galvanizing);

In the present invention, the steel slab composed of the above-described component composition is hot rolled according to a conventional method and wound at 750 ° C or lower.

Next, the hot rolled steel sheet obtained above is pickled and descaled.

The steel sheet thus obtained may be used for the annealing and plating step of the following step as it is, or may be used for the annealing and plating step after cold rolling.

That is, the base steel plate (: substrate steel sheet) of the plated steel sheet of the present invention may be either a hot rolled steel sheet or a cold rolled steel sheet.

When annealing the steel sheet in the annealing furnace, the heating temperature is preferably 750 ° C. or higher, more preferably 750 ° C. or higher, 1000 ° C. or lower, still more preferably 800 ° C. or higher and 1000 ° C. or lower.

When it is less than 750 degreeC, the steel plate surface thickening amount of dioxide elements, such as Mn normally contained in a high tension steel plate, is small, and it concentrates on the surface again just before plating after that.

In addition, in the case of a steel sheet with a high Mn content, such as the steel sheet of the present invention, the concentrated Mn cannot be dispersed in a band-like structure in the base steel sheet, and thus a defect that cannot be plated easily occurs.

Therefore, it is necessary to anneal at 750 ° C. or higher, more preferably 800 ° C. or higher, and to sufficiently surface-concentrate the dioxide element such as Mn of the steel plate base iron surface layer portion.

In addition, when the heating temperature in the annealing furnace exceeds 1000 ° C, since the desired structure and material cannot be obtained because the phase shifts from the α-γ 2 phase, the heating temperature in the annealing furnace is preferably 1000 ° C or lower.

After annealing and cooling, the concentrated layer of the steel component on the surface of the steel sheet is removed by pickling.

The acid of the pickling liquid in pickling is not limited to HCl, H ₂ SO ₄ , HNO ₃ and the like may be used, and the acid type is not particularly limited.

The pH of the pickling liquid at the time of pickling in the subsequent step of the annealing furnace is operated at 1 or less, and in the case of using hydrochloric acid, the concentration of HCl is preferably 1 to 10 wt%.

When the pH of the pickling liquid exceeds 1, the effect of removing surface concentrates by pickling becomes insufficient.

If the concentration of HCl is less than 1 wt%, the effect of removing surface concentrates by pickling is insufficient. If the concentration is more than 10 wt%, the surface of the steel sheet due to overacid washing becomes rough and the raw unit of acid used is unsuitable.

It is preferable that pickling liquid temperature is 40-90 degreeC, and when it is less than 40 degreeC, the removal effect of the surface concentrate by pickling becomes inadequate, and when it exceeds 90 degreeC, the surface of the steel plate by overacid washing becomes rough and unsuitable.

In addition, the pickling liquid temperature is more preferably in the range of 50 to 70 ° C.

The pickling time is preferably 1 to 20 seconds. If the pickling time is less than 1 second, the effect of removing surface concentrates by pickling is insufficient. If the pickling time is longer than 20 seconds, the surface of the steel sheet is roughened and the production time is increased. It becomes long, productivity falls, and it is unsuitable.

And pickling time becomes like this. More preferably, it is the range for 5 to 10 second.

In the present invention, after pickling, the steel sheet treated in each of the above steps is again heated and reduced in a reducing atmosphere, for example, in a heating furnace arranged in a continuous hot dip galvanizing line, followed by hot dip galvanizing.

The oxide film on the surface of the steel sheet produced after pickling (: pickling residue) contains Fe and P, which is poorly soluble due to P in the steel, and cannot be plated unless the P-based oxide film (P-based oxide) is reduced. Can't prevent it.

In addition, since the P-based oxide film is derived from P in the steel, the more P in the steel, the larger the amount of P-based oxide film is produced.

Further, the P-based oxide is generated on the surface of the steel sheet near-phosphate (PO ₄ ^3-), phosphoric acid can sogeun ^{_{(HPO 4 2-, H 2 PO}} 4 -), hydroxyl (OH ^-) and iron ion (Fe ^3+, Fe ^And phosphorus oxides such as iron phosphate compounds having ²⁺ ) as main components and P ₂ O ₅ and P ₄ O ₁₀ .

Moreover, the following iron phosphate compound is illustrated as said iron phosphate compound.

Iron phosphate compounds: Fe ^III (PO ₄ ) · nH ₂ O, Fe ^III ₂ (HPO ₄ ) ₃ nH ₂ O, Fe ^III (H ₂ PO ₄ ) ₃ nH ₂ O, Fe ^II ₃ (PO ₄ ) ₂ NH ₂ O, Fe ^II (HPO ₄ ) nH ₂ O, Fe ^II (H ₂ PO ₄ ) ₂ nH ₂ O, Fe ^III (HPO ₄ ) (OH) nH ₂ O, Fe ^III ₄ {(PO ₄ ) (OH)} ₃ nH ₂ O (n is an integer of 0 or more)

In addition, phosphorus oxide and iron phosphate compounds are reduced under the same degree of reducing conditions.

In the present invention, by controlling the conditions under which the P-based oxide film is reduced precisely thermodynamically, the plating is prevented.

That is, the present inventors used various steel plates which differ in P content in steel, and investigated the heat reduction temperature and reducing atmosphere with favorable plating property in each.

As a result, the P-based oxide film is reduced under the condition that the P-based oxide film is thermodynamically reduced, and the heat-reduction temperature is too high to prevent concentration of dioxide elements such as Mn on the surface, thereby preventing plating. It can be operated under the correct plating conditions.

Then, the heating temperature in the heat reduction when the hot-dip galvanizing: t ₁ (℃) the steel P content: by P satisfies the following formula (1) for (wt%) oxide film P system is reduced, and heat-reducing It was found that the temperature was too high to prevent concentration of Mn again on the surface, thereby preventing the plating from being performed and operating under the correct plating conditions.

{[P(wt%)+(2/3)]×1100}/{t₁ (℃)}

1.1 …(1)0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}

1.1... (One)

That is, in the steel plate containing 0.1 wt% or less of P concerning this invention, when there is much P content in steel, heat reduction temperature should be raised by that much.

However, as in the case where the Mn content in the steel is 1.0 wt% or more, for example, when the content of the dioxide element in the steel is large, the heating temperature in the heat reduction: t ₁ (° C.) and the P content in the steel: P (wt%) When the relationship satisfies the following formula (1-1), plating occurs due to the surface thickener because a dioxide element such as Mn causes surface thickening again at the time of heat reduction.

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)} <0.9. (1-1)

In addition, when the relationship between heating temperature: t ₁ (° C.) and P content in steel: P (wt%) in heat reduction satisfies the following formula (1-2), the reduction of the P-based oxide film is insufficient and plating is performed. You can't prevent things that don't work.

1.1 <{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}. (1-2)

In practical operation, plating can be prevented if it is the range of +/- 10% with respect to the upper limit and the lower limit of the said optimum heat reduction temperature range.

The heat reduction atmosphere is an area capable of reducing the P-based oxide film, and an appropriate dew point and hydrogen concentration should be selected according to the elin gum diagram. However, since the reduction reaction is a function of the atmosphere and the cracking time during the heat reduction, the actual operation is performed. It is desirable that the phase has a slightly lower dew point and a somewhat higher hydrogen concentration than the thermodynamically required range.

Therefore, the dew point of the atmosphere gas at the time of heat reduction prior to hot dip galvanizing is preferably in the range of -50 ° C to 0 ° C and the hydrogen concentration in the range of 1 to 100 vol%.

When the dew point of the atmosphere gas at the time of heat reduction is high beyond 0 degreeC, since P-type oxide film is not reduced well as mentioned above and heat-reduction is needed for a long time, it is unpreferable.

Moreover, it is industrially difficult to make the dew point of atmospheric gas lower than -50 degreeC, and a dew point is prescribed | regulated as -50 degreeC-0 degreeC.

In addition, when the hydrogen concentration is lower than 1 vol%, the P-based oxide film is not reduced well, which is not preferable because long-term heat reduction is required.

Therefore, the hydrogen concentration at the time of heat reduction before hot dip galvanizing is prescribed | regulated in the range of 1-100 vol%.

As described above, in the present invention, the dew point, hydrogen concentration, and heating temperature (steel plate temperature) of the atmospheric gas at the time of heat reduction are controlled so that the P-based oxide film derived from P in steel can be reduced in the reducing atmosphere of the P-based oxide film. In addition, when there are many dioxide elements, such as Mn, the annealing temperature is not raised too much and the amount of surface concentrates is suppressed, and plating is prevented.

II.-3: Manufacturing conditions in the case of a one-stage heat treatment method (: heating reduction → hot dip galvanizing);

In the present invention, the steel slab composed of the above-described component composition is hot rolled according to a conventional method and wound at 750 ° C or lower.

Next, the hot rolled steel sheet obtained above is pickled and descaled.

The steel sheet thus obtained is subjected to the following formula (2) at a heating temperature: T of at least 750 ° C. and at most 1000 ° C. after pickling or after cold rolling, and the dew point of the atmosphere gas: t is the following formula (3) The molten zinc plating is performed after heating in an atmosphere having a hydrogen concentration of 1 to 100 vol%.

{[P(wt%)+(2/3)]×1150}/{T(℃)}

1.15 …(2)0.85

{[P (wt%) + (2/3)] × 1150} / {T (° C)}

1.15. (2)

{[P(wt%)+(2/3)]×(-30)}/{t(℃)}

1.8 …(3)0.35

{[P (wt%) + (2/3)] × (-30)} / {t (° C)}

1.8... (3)

When the annealing temperature is less than 750 ° C., C and Mn concentrated in the band-shaped second phases (mainly cementite, pearlite and bainite, and only a part of martensite and residue austenite) in the base material cannot be dispersed, thereby preventing plating. In order to generate a defect, the heating temperature is set at 750 ° C or higher.

Moreover, when heating temperature exceeds 1000 degreeC, desired structure and material cannot be obtained in order to escape the (alpha)-(gamma) 2 phase range.

It is for the following reason that the heating temperature should be increased as shown in Equation (2) as the amount of P in the steel increases.

That is, when the hot rolled steel sheet is pickled, the P-based oxide, which is a Fe-P-based pickling residue, is formed as the iron is eluted on the surface of the steel sheet, and the temperature must be raised to completely reduce the residue and improve the plating property.

The amount of P-based oxide produced is almost proportional to the amount of P in the steel.

Therefore, as the amount of P in the steel increases, the heating temperature must be increased as in Equation (2) above.

On the other hand, when the heating temperature is increased, the surface thickening amount of the dioxide alloy element for strengthening the solid solution such as Mn increases and the plating property is deteriorated. Therefore, the above-mentioned surface thickening must be thermodynamically suppressed by lowering the dew point of the atmospheric gas during heating. do.

Therefore, as the amount of P in the steel increases, the dew point of the atmospheric gas at the time of heating must be reduced as in the above formula (3).

In addition, when the hydrogen concentration in the atmosphere gas at the time of heating is less than 1 vol%, it is not preferable because P-type oxide is not reduced well thermodynamically and heating is required for a long time.

Therefore, the hydrogen concentration in atmospheric gas at the time of heating is prescribed | regulated to 1-100 vol%.

As described above, after heating under a condition in which the heating atmosphere is precisely controlled in the hot-dip galvanizing line without heating in the annealing furnace, hot-dip galvanizing allows good plating and plating adhesion with or without Mo addition. It can be secured.

As described above, good plating property is achieved by simultaneously controlling the heating temperature (steel plate temperature), the dew point of the atmosphere gas, and the hydrogen concentration so that both the reduction of the Fe-P-based pickling residue and the suppression of the surface concentration of the components in the steel are simultaneously achieved. , Plating adhesion can be secured.

Therefore, according to this invention, favorable plating property and plating adhesiveness can be ensured even without the annealing process before a hot-dip galvanizing line board | plate.

II.-4: Manufacturing conditions of hot dip galvanizing and heat alloying treatment method;

In the present invention, after heating and reducing the base steel sheet as described above, hot dip galvanizing is performed in a hot dip galvanizing bath.

For the hot dip galvanizing bath, a plating bath containing 0.08 to 0.2 wt% of Al is suitable, and a bath temperature of 460 to 500 ° C is suitable.

Moreover, when penetrating into a bath, the steel plate temperature is suitable for 460-500 degreeC.

In addition, it is preferable that the plating adhesion amount of a hot-dip galvanized steel plate is 20-120 g / m <2> as an adhesion amount per steel plate surface.

If the plating deposition amount of the hot-dip galvanizing is less than 20 g / ㎡, the corrosion resistance is lowered. On the contrary, when the plating adhesion amount is more than 120 g / ㎡, the effect of improving the corrosion resistance is practically saturated and not economical.

In addition, the adhesion amount per one surface of the steel sheet means the adhesion amount per unit area divided by the plating adhesion amount by the plating adhesion area.

That is, in the case of conventional double-sided plating, the adhesion amount per unit area divided by the plating adhesion amount is shown. In the case of single-sided plating, the adhesion amount per unit area divided by the plating unit area of the cross section is shown.

The present inventors have found that, when alloying the hot-dip galvanized steel sheet manufactured as mentioned above, investigated the conditions to be improved the plating adhesion after alloying example results, alloying temperature: t ₂ (℃) the steel P content: P ( wt%) and Al content in the bath during hot dip galvanization: When the following formula (4) is satisfied for Al (wt%), alloying proceeds sufficiently and the deterioration of plating adhesion due to overalloy can be suppressed. Turned out.

[7×{100×[P(wt%)+(2/3)]+ 10×Al(wt%)}]/[t₂ (℃)]

1.05 …(4)0.95

[7 × {100 × [P (wt%) + (2/3)] + 10 × Al (wt%)}] / [t ₂ (° C.)]

1.05... (4)

That is, the steel P segregates at the grain boundaries of the iron and iron to delay the alloying reaction. If the P content is high in the steel, the alloying reaction proceeds only when the alloying temperature is increased.

And when there is little P content in steel, when an alloying temperature is raised too much, plating adhesiveness will deteriorate with overalloy.

In addition, when the amount of Al in the hot dip galvanizing bath is large, a large amount of Fe—Al alloy layer is formed on the surface of the steel sheet immediately after plating, thereby increasing the temperature required for alloying.

In addition, when the amount of Al in the bath is small, if the alloying temperature is not suppressed, there is a fear of causing deterioration in plating adhesion due to overalloy.

As described above, in order to ensure good plating adhesion, the alloying temperature: t ₂ (° C) is determined according to the P content in the steel: P (wt%) and the Al content in the bath during hot dip galvanizing: Al (wt%) and alloyed. Should be.

In the present invention, the alloying temperature: t ₂ (℃) is a heat alloying treatment that satisfies the following formula (4) for the P content in the steel: P (wt%) and Al content: Al (wt%) in the bath during hot dip galvanizing. It is desirable to.

1.05 …(4)0.95 [7 × {100 × [P (wt%) + (2/3)] + 10 × Al (wt%)}] / [t ₂ (° C.)]

1.05... (4)

Alloying temperature: For satisfying the t ₂ (℃) is the following formula (4-1), it is irrelevant, since the coating adhesion deteriorates, depending on the alloy.

[7 × {100 × [P (wt%) + (2/3)] + 10 × Al (wt%)}] / [t ₂ (° C.)] <0.95. (4-1)

The alloying temperature: t ₂ (℃) is to require the following formula (4-2) occurs for a long time such as hours or alloyed alloy is insufficient, and baked deviation when satisfying the irrelevant in terms of productivity.

1.05 <[7 × {100 × [P (wt%) + (2/3)] + 10 × Al (wt%)}] / [t ₂ (° C.)]. (4-2)

As described above, the heat alloying treatment in the present invention is characterized in that the alloying temperature after hot-dip galvanizing is controlled according to the P content in the base steel sheet and the amount of Al in the bath during hot-dip galvanizing to ensure optimum plating adhesion. .

In practical operation, plating adhesion can be ensured if it is a range of +/- 5% with respect to the upper limit and the lower limit of the optimum alloying temperature range.

The Fe diffusion amount in the plating layer at the time of alloying process mentioned above needs to be taken as 8-11 wt% as Fe content in the obtained plating layer.

When it is less than 8 wt%, baking deviation and the like occur, as well as deterioration of the sliding property due to insufficient alloying, and when it exceeds 11 wt%, plating adhesion deteriorates with overalloy.

In this invention, it is preferable that Fe content in the plating layer after alloying process is 9-10 wt%.

On the other hand, the addition of Mo to the base steel sheet not only improves the plating adhesion and the like, but also the amount of Mo diffusion into the plating layer during alloying of the hot-dip galvanized steel sheet containing Mo as the base steel sheet is 0.002 to 0.11 wt. It was found that the corrosion resistance is good when the% is satisfied.

It is because Mo is an element which is harder to oxidize than Fe, and slight diffusion and addition of Mo in a plating layer improve corrosion resistance.

In this invention, it is preferable that Mo diffusion amount in the plating layer at the time of alloying process is 0.002-0.11 wt% in Mo content in the obtained plating layer.

If the content is less than 0.002 wt%, the effect of improving the corrosion resistance is insufficient. On the contrary, if the content exceeds 0.11 wt%, the Mo content in the base steel sheet must be more than 1.0 wt% in order to secure the Mo content in the plating layer, which is not economically desirable.

In addition, when the P-based oxide film is unreduced at the time of heat reduction immediately before plating, diffusion of Mo into the plating layer tends to be suppressed.

When the P-based oxide film is completely reduced at the time of heat reduction, plating adhesion and the like are improved, but in Mo-added steel, the effect of promoting diffusion of Mo into the plating layer can be obtained by reduction of the P-based oxide film. As a result, it was found that the effect of improving the corrosion resistance of the alloyed hot dip galvanized steel sheet can also be obtained.

As described above, according to the present invention, an alloyed hot-dip galvanized steel sheet obtained by hot-dip galvanizing a steel sheet containing 1.00 wt% or less of Mo, wherein the Fe content in the alloyed hot-dip galvanized layer is 8-11 wt%. It can be seen that the alloyed hot dip galvanized steel sheet having a Mo content of 0.002 to 0.11 wt% is a high strength alloyed hot dip galvanized sheet having excellent plating adhesion and corrosion resistance.

The steel sheet containing 1.00 wt% or less of Mo is preferably a steel sheet containing 0.01 to 1.00 wt%, more preferably 0.05 to 1.00 wt%, still more preferably 0.05 to 0.5 wt%. It is preferable.

In the present invention, the plating deposition amount of the alloyed hot-dip galvanized steel sheet is preferably 20 to 120 g / m 2 as the deposition amount per sheet of steel sheet as defined above.

If the plating adhesion amount of the alloyed hot dip galvanizing is less than 20 g / m 2, the corrosion resistance is lowered. On the contrary, if the plating adhesion amount is more than 120 g / m 2, the effect of improving the corrosion resistance is practically saturated and not economical.

On the other hand, the plating adhesion amount of the alloying hot-dip zinc plating as the diffusion layer of the metal can be measured by analyzing the plating solution obtained by dissolving the plating layer in an alkali-containing solution such as NaOH or KOH or an acid-containing solution such as HCl or H ₂ SO ₄ . Can be.

Fig. 1 is a graph showing the relationship between tensile strength TS, yield ratio YR and TS × El balance of a steel sheet and [average thickness Tb / plate thickness T] of a band-shaped second phase.

Fig. 2 is an example of a micrograph (a) of a metal structure showing a representative band-like second phase structure and a schematic diagram (b) of the metal structure.

3 is an example of the micrograph (a) of the metal structure and the schematic diagram (b) of the metal structure which showed the state in which the 2nd phase structure was disperse | distributed by 1st heating.

4 is a graph showing the relationship between the P content in the steel and the optimum heat reduction temperature range in which defects that cannot be plated do not occur.

Fig. 5 is a graph showing the hydrogen concentration of the atmospheric gas and the optimum region of the dew point at the time of heat reduction in which a defect which is not plated does not occur.

6 is a graph showing the relationship between the P content in the steel and the optimum alloying temperature range having good plating adhesion.

7 is a graph showing the relationship between Mo content and corrosion loss in the plating layer.

FIG. 8 is a graph showing the relationship between the P content in steel and the optimum heat reduction temperature range in which defects that cannot be plated do not occur.

FIG. 9 is a graph showing the optimum region of the dew point of the atmospheric gas at the time of heat reduction in which P content in steel and defects which cannot be plated do not occur.

Hereinafter, the present invention will be described in more detail based on Examples.

[Example 1] (Invention Examples 1 to 20, Comparative Examples 1 to 12) [: Dispersion of Band Structure in Steel Sheet]

The continuous casting slab having a thickness of 300 mm of the chemical composition (steel type: A to Q) shown in Table 1 was heated to 1200 ° C. and roughly rolled in two passes, followed by hot rolling with a thickness of 2.3 mm using a seven-stage finishing mill. It is wound up as a steel plate.

After pickling the hot rolled steel sheet obtained above, the experiment numbers 1, 9, 11, 12, 17, 19, 20, 27, 28, and 29 were subjected to the hot rolled steel sheets, and the experiment numbers 2 to 8, 10, 13 to For 16, 18, 21 to 26, and 30 to 32, cold rolling is performed at a plate thickness of 1.0 mm, followed by heating in a continuous annealing line (1 time heating), pickling in continuous hot dip galvanizing, and heating (1 time heating or 2 times). Heating), galvanizing and, in some cases, alloying again.

Types of steel: Other parts of C to E are electro galvanized after heating 1.0 mm cold rolled steel sheet in a continuous annealing line.

Each of the above manufacturing conditions is shown in Tables 2 and 3.

The obtained steel sheet is examined for mechanical properties, plating properties, alloying treatment properties, spot weldability, and the like as test materials.

Then, after heating (single-time heating) in a continuous annealing line or continuous hot dip galvanizing, the structure of the steel sheet was observed to determine the ratio (T _b ) of the thickness (T _b ) of the band-like structure composed of the second phase to the plate thickness (T _b ). / T) is measured.

On the other hand, the thickness T _b of band structure | tissue is calculated | required by following formula (5) by measuring the thickness of the band structure | tissue which consists of all the 2nd phases of the plate thickness direction in the image of 1500 times magnification with an image analyzer.

T_bi/n …(5)Thickness of banded tissue (T _b ) =

T _bi / n… (5)

And in said formula (5)

T_bi : 판두께 방향의 밴드형 조직의 각 두께의 합계

T _bi : Sum of the thicknesses of the band-like structures in the plate thickness direction

n: number of band-like structures in plate thickness direction

Moreover, plating property, alloying processability, and spot weldability are evaluated by the following method.

[Gapability:]

It is judged visually that it is "good" that there is no plating at all, "good" that there is some thing which cannot be plated, and what is remarkable that it is not plating is "inferior".

[Alloy alloy:]

It is judged visually that "excellent" that there is no alloying deviation at all, "good" what has a slight alloying deviation, and that "the inferiority" which alloying deviation is remarkable is visually.

[Spot weldability:]

Tensile shear test of spot welded seam is carried out according to JIS Z 3136 method, 6700 N for sheet thickness 1.0 mm and 23000 N for plate thickness 2.3 mm, respectively. "Excellence", lower than the lower limit of the strength is "inferior".

All the obtained measurement results are shown in Table 2 and FIG.

In Tables 1 to 3, Inventive Examples 1 to 20 show a low yield ratio, a good TS × E1 balance, and no particular problems with regard to plating property, alloying treatment property, and spot weldability.

EXAMPLE 2 (Invention Examples 21-37, Comparative Examples 13-21) [: Two-stage heating and pickling treatment method]

After the continuous cast slab having a thickness of 300 mm of the chemical composition (steel type: A to D, DD, F to I, K to N, R to X) shown in Table 1 was heated to 1200 ° C. and roughly rolled in three passes, It is rolled by the finishing mill of 7 stands, and the hot rolled steel plate whose thickness is 2.3 mm is obtained.

It winds up at the temperature (: CT) shown in Table 4 and Table 5 after that.

After pickling the obtained hot rolled steel sheet, the test numbers 33, 43 to 49, and 52 to 54 were mailed to the continuous annealing line according to the hot rolled steel sheet, and the test numbers 34 to 42, 50, 51, and 55 to 58 were After cold-rolling so that plate | board thickness may be 1.0 mm, it is sent to the continuous annealing line and annealed at the heating temperature shown in Table 4, Table 5.

Thereafter, the obtained rolled steel sheet of each steel type is mailed to a continuous hot dip galvanizing line and subjected to pickling, heat reduction, hot dip galvanizing, and heat alloying treatment under various conditions shown in Tables 4 and 5 (Invention Examples 21 to 23). Invention Examples 25-37, Comparative Examples 13-21).

Moreover, in Invention Example 24, the performance of the obtained hot-dip galvanized steel sheet is evaluated based on the evaluation method and evaluation criteria mentioned later, without performing a heat alloying process.

In addition, conditions other than the manufacturing conditions shown in Table 4 and Table 5 are shown to (1)-(3) below.

(1) Pickling in a continuous hot dip galvanizing line:

The pickling in the continuous hot dip galvanizing line shown in Table 4 and Table 5 was carried out at an acid temperature of 60 ° C., HCl concentration of 5 wt%, or at an acid temperature of 60 ° C. or at a liquid temperature of 60 ° C. and H ₂ SO ₄ concentration. : The experiment was performed by pickling for 5 seconds using a 5 wt% pickling solution (pH: 1 or less), but the plating performance was shown to be improved under any conditions.

(2) heat reduction in a continuous hot dip galvanizing line:

The heat reduction in the continuous hot dip galvanizing line shown in Table 4 and Table 5 was carried out under an H ₂ -N ₂ gas atmosphere of H ₂ concentrations shown in Table 4 and Table 5.

(3) Plating adhesion amount of hot dip galvanizing, plating adhesion amount of alloyed hot dip galvanizing:                 

The plating adhesion amount of the hot dip galvanizing of Inventive Example 24 which did not carry out the heat alloying process shall be 40 g / m <2> on both surfaces of a steel plate.

Moreover, the plating adhesion amount of alloying hot-dip galvanizing is in the range of 30-60 g / m <2> in both steel plate both surfaces (Invention Examples 21-23, Invention Examples 25-37, Comparative Examples 13-21).

Next, the plating property, plating adhesion, appearance after alloying, alloying degree, corrosion resistance, workability, spot weldability, etc. of the obtained hot dip galvanized steel sheet and alloyed hot dip galvanized steel sheet are evaluated based on the following evaluation methods and evaluation criteria.

The obtained evaluation results are shown in Table 6 and Table 7.

In addition, the presence or absence of P type | system | group reduction of Table 4 and Table 5 is analyzed by ESCA (: photoelectron spectroscopy), and it judges according to whether the peak of P compound considered to couple | bond with oxygen is recognized clearly. It was.

And, that is thought to be associated with the oxygen compound is a phosphoric acid P muscle (PO ₄ ^3-), sogeun can phosphate ^{_{(HPO 4 2-, H 2 PO}} 4 -), hydroxyl (OH ^-) and iron ion (Fe ^{3 + And} Fe ²⁺ ) are the following iron phosphate compounds.

Iron phosphate compounds: Fe ^III (PO ₄ ) · nH ₂ O, Fe ^III ₂ (HPO ₄ ) ₃ nH ₂ O, Fe ^III (H ₂ PO ₄ ) ₃ nH ₂ O, Fe ^II ₃ (PO ₄ ) ₂ NH ₂ O, Fe ^II (HPO ₄ ) nH ₂ O, Fe ^II (H ₂ PO ₄ ) ₂ nH ₂ O, Fe ^III (HPO ₄ ) (OH) nH ₂ O, Fe ^III ₄ {(PO ₄ ) (OH)} ₃ nH ₂ O (n is an integer of 0 or more)

3N 의 관계를 만족시키는 경우에 피크가 명료하게 인정되는 것으로 하였다.In addition, ESCA is measured by the law and focuses on the spectral intensity of P at a position which is thought to bind with O corresponding to the iron phosphate compound described above as an example in a general spectrum collection, and the peak height is noise other than the peak. The height H from the base of the peak position is H compared to the average amplitude N of the portions.

The peak was clearly recognized when the relationship of 3N was satisfied.

[Gapability:]

The appearance of the plated steel sheet (non-alloyed hot dip galvanized steel sheet) after hot dip galvanizing was visually evaluated.

: 도금이 안되는 결함 없음 (도금성 양호)

: No plating defect (good plating)

×: Defects not plating

[Plating Adhesion:]

After bending the plated steel sheet 90 degrees, the plated layer on the compression side was peeled off with cellophane tape, and evaluated by the amount of the plated film adhered to the cellophane tape.

(Unalloyed Plated Steel Sheet)

: 도금층의 박리 없음 (도금 밀착성 양호)

: No peeling off of plating layer (good plating adhesion)

X: peeling of the plating layer (poor adhesion)

(Coated Steel Plate)

: 도금 박리량이 적음 (도금 밀착성 양호)

: Low plating peeling amount (good plating adhesion)

×: high plating peeling amount (poor adhesion)

[Appearance after alloying:]                 

Evaluate visually.

: 합금화 편차가 없어 균일한 외관을 얻을 수 있음

: There is no deviation of alloying to get a uniform appearance

×: alloying deviation occurs

Alloying degree, Mo diffusion amount:

The Fe content and Mo content in the alloying hot dip galvanized layer are analyzed and measured by analysis of a solution obtained by dissolving the plating layer by a general plating layer dissolution method using an alkaline solution or an acidic solution.

[Processability:]

590 MPa 이면서 El

30 % 을 만족시키는 것을 양호로 하고 그 이외의 것을 불량으로 한다.TS

El 590 MPa

Satisfying 30% is made good and other than that is made defective.

[Corrosion resistance:]

The corrosion resistance test is evaluated by the loss of corrosion by the salt spray test (SST).

The presence or absence of the effect of improving corrosion resistance is evaluated in comparison with an alloyed hot dip galvanized steel sheet based on Mo-free steel.

[Spot weldability:]

Press force: 2.01 kN, current: 3.5 kA, energization time: Ts = 25cyc, Tup = 3cyc., Tw = 8cyc, Th = 5cyc., To = 50cyc., Tip: DR6φ spherical body for direct spot welding It is made into the excellent thing, and the thing which cannot be welded is made into defect.

As shown in Tables 6 and 7, the alloyed hot-dip galvanized steel sheets of Inventive Examples 21 to 23 and Inventive Examples 25 to 37, which were produced by the production method of the present invention, did not generate defects that were not plated. At the same time, there was no problem in plating adhesion, appearance after alloying, workability and spot weldability.

In addition, even the hot-dip galvanized steel sheet of the present invention 24 did not cause defects that could not be plated, and was excellent in plating property and had no problems with plating adhesion, workability, and spot weldability.

On the other hand, in the alloyed hot dip galvanized steel sheets of Comparative Examples 13 to 21, since the heat reduction temperature prior to hot dip galvanizing, the alloying temperature, alloying degree or steel composition during hot alloying after hot dip galvanizing are different from the conditions of the present invention. Incorrect plating or defects in plating quality or processability.

In addition, a plated steel sheet (Comparative Example 14) using a base metal sheet without Mo is difficult to reduce the P-based oxide, and is poor in terms of mechanical properties (processability) as well as plating properties and plating adhesion.

In addition, the corrosion resistance of the plated steel sheet containing Mo in the plated layer does not contain Mo in the plated layer or the amount of corrosion is lower than that of the plated steel sheet (Comparative Example 13, Comparative Example 14). It can be seen that the corrosion inhibitory effect can be obtained.

Example 3 (Invention Examples 38 to 46, Comparative Example 22) [: 1-stage heat treatment method]

Inventive Examples 21-23 and Inventive Examples 25-37 described above were the same as those of Inventive Examples 21-23 and Inventive Examples 25-37 except that annealing before continuous hot dip galvanizing line mailing and no pickling were performed in the continuous hot dip galvanizing line. The hot-rolled steel sheet of each steel type by the method to the continuous hot-dip galvanizing line, and subjected to heat reduction, hot-dip galvanizing, alloying treatment, hot-dip galvanized steel sheet (: unalloyed hot-dip galvanized steel sheet) and alloyed molten The galvanized steel sheet was evaluated in the same manner as Inventive Examples 21 to 23 and Inventive Examples 25 to 37.

The manufacturing conditions are shown in Table 8, and the obtained evaluation results are shown in Table 9.

In addition, the plating adhesion amount of alloying hot-dip galvanizing is all in the range of 30-60 g / m <2> on both surfaces of a steel plate.

As shown in Tables 8 and 9, defects that cannot be plated in the hot-dip galvanized steel sheet are caused by keeping the heating temperature, the dew point of the atmospheric gas, and the hydrogen concentration in the continuous hot dip galvanizing line within the scope of the present invention. In addition, the alloyed hot-dip galvanized steel sheet excellent in plating adhesion, alloying appearance and workability can be produced (Invention Examples 38 to 46).

On the other hand, when the above conditions do not satisfy the scope of the present invention, a defect that cannot be plated occurs (Comparative Example 22).

As described above, according to the present invention, it is possible to provide a high strength steel sheet having no problem in plating property, low yield ratio, and good TS x El balance.

In addition, according to the present invention, it is possible to provide a high strength hot dip galvanized steel sheet and a high strength alloyed hot dip galvanized steel sheet, which prevent occurrence of unplated defects, are excellent in workability and plating adhesion, and are excellent in corrosion resistance.

As a result, by applying the high-strength thin steel sheet and the plated steel sheet of the present invention, it is possible to reduce the weight and fuel efficiency of the automobile, and further contribute to the improvement of the global environment.

Claims (23)

C: 0.01-0.20 wt%, Si: 1.0 wt% or less, Mn: 1.0-3.0 wt%, P: 0.10 wt% or less, S: 0.05 wt% or less, Al: 0.10 wt% or less, N: 0.010 wt% or less, Cr: 1.0 wt% or less, Mo: 0.001-1.00 wt% Containing, and the remaining portion is composed of Fe and inevitable impurities, and the band-like structure composed of the second phase is T _b / T

A high strength steel sheet excellent in workability and plating property, characterized by a thickness satisfying a relationship of 0.005 (T _b : average thickness in the thickness direction of the band-like structure, T: steel sheet thickness). The high strength steel sheet further comprises one or two or more selected from Nb: 0.001-1.0 wt%, Ti: 0.001-1.0 wt%, and V: 0.001-1.0 wt%. High strength steel sheet with excellent workability and plating. C: 0.01-0.20 wt%, Si: 1.0 wt% or less, Mn: 1.0-3.0 wt%, P: 0.10 wt% or less, S: 0.05 wt% or less, Al: 0.10 wt% or less, N: 0.010 wt% or less, Cr: 1.0 wt% or less, Mo: 0.001-1.00 wt% Workability and plating property, wherein the remaining part is hot rolled to a slab composed of Fe and an unavoidable impurity, wound at 750 ° C. or lower, and then heated to 750 ° C. or higher and 1000 ° C. or lower and then cooled. Excellent high strength steel sheet manufacturing method. C: 0.01-0.20 wt%, Si: 1.0 wt% or less, Mn: 1.0-3.0 wt%, P: 0.10 wt% or less, S: 0.05 wt% or less, Al: 0.10 wt% or less, N: 0.010 wt% or less, Cr: 1.0 wt% or less, Mo: 0.001-1.00 wt% Workability and plating, characterized in that the residue is hot-rolled to a slab composed of Fe and an unavoidable impurity composition and wound at 750 ° C. or lower, followed by cold rolling, and then heated to 750 ° C. or higher and cooled. Method for producing high strength steel sheet with excellent properties. The processability and plating property according to claim 3 or 4, further comprising hot-dip galvanizing during the step of cooling after heating to 750 DEG C or higher, or further heat-alloying after hot-dip galvanizing. Method for producing high strength steel sheet. The method according to claim 3 or 4, wherein after heating to 750 DEG C or higher, cooling is carried out, and then again heated to 700 to 850 DEG C, followed by hot dip galvanizing or hot dip galvanizing during cooling. Process for producing a high strength steel sheet excellent in workability and plating properties, characterized in that the treatment. The slab according to claim 3 or 4, wherein the slab further contains one or two or more selected from Nb: 1.0 wt% or less, Ti: 1.0 wt% or less, V: 1.0 wt% or less. Manufacturing method of high strength steel sheet excellent in workability and plating property. 4. The method of claim 3, wherein the product is wound up at 750 DEG C or less and then pickled, then heated to 750 DEG C or more in an annealing furnace, cooled, and then pickled, followed by reduction of P-based oxide which is a pickling residue on the surface of the steel sheet. A method of producing a high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, characterized by performing hot dip galvanization after heat reduction under conditions. 4. The method of claim 3, wherein the product is wound up at 750 DEG C or less and then pickled, then cold rolled, heated to 750 DEG C or more in an annealing furnace, cooled, and then pickled remaining on the surface of the steel sheet. A method of producing a high strength hot dip galvanized steel sheet having excellent workability and plating adhesion, characterized by performing hot dip galvanizing after heating under reduced conditions of a P-based oxide as water. The process of claim 3, wherein the product is wound up at 750 DEG C or less and then pickled, then heated to 750 DEG C or more in an annealing furnace, cooled, and then pickled, followed by dew point of atmospheric gas: -50 DEG C to 0 DEG C, Hydrogen concentration of the atmosphere gas: hot-dip galvanized after heat reduction under a condition of 1 to 100 vol%, characterized in that the high-strength hot-dip galvanized steel sheet excellent in workability and plating adhesion. The process according to claim 3, wherein the product is wound up at 750 DEG C or less and then pickled, then cold rolled, heated to 750 DEG C or more in an annealing furnace, cooled and then pickled, and then the dew point of the atmosphere gas:- Process for producing high strength hot dip galvanized steel sheet excellent in processability and plating adhesion, characterized by performing hot dip galvanizing after heating and reducing under a hydrogen concentration of 50 ° C. to 0 ° C. and an atmospheric gas of 1 to 100 vol%. 4. The method of claim 3, wherein the product is wound up at 750 DEG C or lower and then pickled, then heated to 750 DEG C or higher in an annealing furnace, cooled and then pickled, and then the heat reduction temperature: t ₁ (DEG C) is P in the steel. Content: The method of manufacturing a high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, characterized by performing hot dip galvanizing after heat reduction under conditions satisfying the following formula (1) with respect to P (wt%). 0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}

1.1... (One) 4. The method of claim 3, wherein the product is wound up at 750 DEG C or lower and then pickled, then cold rolled, heated to 750 DEG C or higher in an annealing furnace, cooled and then pickled, and then heated and reduced in temperature: t ₁ High-strength hot-dip galvanized steel sheet excellent in workability and plating adhesion characterized by performing hot dip galvanizing after heating and reducing under a condition satisfying the following formula (1) for P content in steel: P (wt%) Manufacturing method. 0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}

1.1... (One) The process according to claim 3, wherein the product is wound up at 750 DEG C or less and then pickled, then heated to 750 DEG C or more in an annealing furnace, cooled, and then pickled, followed by dew point of atmospheric gas: -50 DEG C to 0 DEG C, Hydrogen concentration of atmospheric gas: 1 to 100 vol%, heat reduction temperature: t ₁ (° C.) after heat reduction under conditions satisfying the following formula (1) with respect to P content in steel: P (wt%); Process for producing a high strength hot dip galvanized steel sheet excellent in workability and plating adhesion, characterized in that the plating. 0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}

1.1... (One) The process according to claim 3, wherein the product is wound up at 750 DEG C or less and then pickled, then cold rolled, heated to 750 DEG C or more in an annealing furnace, cooled and then pickled, and then the dew point of the atmosphere gas:- 50 ° C to 0 ° C, hydrogen concentration of the atmosphere gas: 1 to 100 vol%, heating reduction temperature: t ₁ (° C) is heated under the condition that the following formula (1) is satisfied for P content in the steel: P (wt%) A method for producing a high strength hot dip galvanized steel sheet excellent in workability and plating adhesion characterized by performing hot dip galvanizing after reduction. 0.9

{[P (wt%) + (2/3)] × 1100} / {t ₁ (° C.)}

1.1... (One) The acid pickling method according to any one of claims 8 to 15, wherein the pickling method is carried out after heating and cooling to 750 ° C. or higher in the annealing furnace.

1, Liquid temperature: It is an pickling method for pickling for 1 to 20 seconds in a pickling solution at 40 to 90 ℃, characterized in that the workability and plating adhesion excellent manufacturing method of high strength hot-dip galvanized steel sheet. After winding up at 750 degreeC or less, pickling is carried out, heating temperature: T satisfy | fills following formula (2) at 750 degreeC or more and 1000 degrees C or less, The dew point of atmospheric gas: A method for producing a high strength hot dip galvanized steel sheet excellent in processability and plating adhesion, which satisfies the following formula (3) and is heated in an atmosphere having a hydrogen concentration of 1 to 100 vol%, followed by hot dip galvanizing. 0.85

{[P (wt%) + (2/3)] × 1150} / {T (° C)}

1.15. (2) 0.35

{[P (wt%) + (2/3)] × (-30)} / {t (° C)}

1.8... (3) The method according to claim 3, wherein after winding at 750 DEG C or lower, pickling and then cold rolling, heating temperature: T satisfies the following formula (2) at 750 DEG C or higher and 1000 DEG C or lower, and an atmospheric gas: Dew point of t: A high strength hot dip galvanized steel sheet having excellent workability and plating adhesion, characterized in that the following formula (3) is satisfied and heated in an atmosphere having a hydrogen concentration of 1 to 100 vol%, followed by hot dip galvanizing. Manufacturing method. 0.85

{[P (wt%) + (2/3)] × 1150} / {T (° C)}

1.15. (2) 0.35

{[P (wt%) + (2/3)] × (-30)} / {t (° C)}

1.8... (3) 19. The slab according to any one of claims 8 to 15, 17 or 18, wherein the slab is further selected from Nb: 1.0 wt% or less, Ti: 1.0 wt% or less, V: 1.0 wt% or less. A method for producing a high strength hot-dip galvanized steel sheet excellent in workability and plating adhesion, characterized by containing two or more species. The hot-dip galvanized steel sheet obtained by the method for producing a high strength hot-dip galvanized steel sheet according to any one of claims 8 to 15, 17 or 18 is subjected to heat alloying again. Process for producing high strength alloyed hot dip galvanized steel sheet with good adhesion. 19. The hot-dip galvanized steel sheet obtained by the method for producing the high strength hot-dip galvanized steel sheet according to any one of claims 8 to 15, 17 or 18 is subjected to a heat alloying treatment and further subjected to the heat alloying treatment. Alloying temperature of t ₂ (° C.), which satisfies the following formula (4) for P content in steel: P (wt%) and Al content in the bath at the time of hot dip galvanizing: Al (wt%). Process for producing high strength alloyed hot dip galvanized steel sheet with excellent workability and plating adhesion. 0.95

[7 × {100 × [P (wt%) + (2/3)] + 10 × Al (wt%)}] / [t ₂ (° C.)]

1.05... (4) 21. The workability and plating adhesion according to claim 20, wherein the slab further contains one or two or more selected from Nb: 1.0 wt% or less, Ti: 1.0 wt% or less, V: 1.0 wt% or less. Method for producing this excellent high strength alloyed hot dip galvanized steel sheet. C: 0.01-0.20 wt%, Si: 1.0 wt% or less, Mn: 1.0-3.0 wt%, P: 0.10 wt% or less, S: 0.05 wt% or less, Al: 0.10 wt% or less, N: 0.010 wt% or less, Cr: 1.0 wt% or less, Mo: 0.001-1.00 wt% An alloyed hot dip galvanized steel sheet obtained by hot-dip galvanizing a steel sheet containing palladium, followed by heat alloying, wherein the Fe content in the alloyed hot dip galvanized layer is 8 to 11 wt%, and the Mo content is 0.002 to 0.11 wt%. High strength alloyed hot dip galvanized steel with excellent plating adhesion and corrosion resistance.

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